Mass cytometry permits high-dimensional analysis of single cell suspensions, much like conventional fluorescence-based flow cytometry (see, e.g., Bendall et al., “Single-cell mass cytometry of differential immune and drug responses across a human hematopoietic continuum.”, Science 2011; 332:687-96; and Tanner et al., “Flow cytometer with mass spectrometer detection for massively multiplexed single-cell biomarker assay.”, Pure and Applied Chemistry 2008; 80:2627-2641). For a mass cytometry experiment, a cell sample is incubated with specific metal-containing probes, usually metal-labeled antibodies (Ab), which bind to their cellular targets and report their presence by quantifying the metal associated with the cell during sample acquisition on the mass cytometer. However, usable mass ranges in version 1 and 2 CyTOF platforms (Fluidigm; South San Francisco, Calif.) comprise 92 and 121 mass channels, respectively, which are far from being fully occupied with reagents. Some channels are not suited for reporting of specific probes due to the overlap with the detection of traces of xenon in argon (AM 128-132, 134, 136) or barium (AM 134-138), being an unwanted yet frequent metal contaminant. The use of some elements such as Pb, Hg and Tl appears limited due to their toxicity for cells and eventually users.
There is a general need for better exploitation of the analytical capacity of mass cytometers, and additional channels available for reporting specific probes would be undoubtedly useful.